[ad_1]
Sharks are quite eclectic eaters. They will tackle prey from fish and invertebrates to marine mammals and turtles. A shark may even have a blast on the odd surfer. If they can catch it or pick it up, and that is made of meat, the sharks will usually eat it.
A new study identifying the contents of tiger sharks baby belly (Galeocerdo cuvier) using DNA analysis revealed an unexpected dietary component, namely: terrestrial songbirds.
Yes, like the ones you see in your garden, such as doves, sparrows and meadows.
"Tiger sharks will see an easy meal and grab it, but I was surprised to learn that they were eating songbirds – I supposed they would be seabirds, "said biologist Kevin Feldheim of the Chicago Field Museum.
"This is one of the most interesting projects that has associated the use of DNA to tell a story."
It all started after a small tiger shark off the coast of Mississippi and Alabama spewed landbird feathers – a brown tinker (Toxostoma rufum) during a follow-up survey of shark populations in 2010.
As it was a surprise, a team of researchers from Mississippi State University decided to continue his research. How common was it? The easiest way to determine what an animal likes to eat is to take a look at what is digested in your stomach, that's what the team did.
Subsequently, during monthly surveys conducted between 2010 and 2018, they monitored other strange contents of shark stomach. They carried the sharks on the boat, pumped their stomachs and let the sharks start again. What work, hey. But they managed to collect the contents of the stomach of 105 tiger sharks during this period.
How to spit a shark (Marcus Drymon)
Indeed, in the stomach of 41 of these sharks, there was a whole bunch of partially digested songbirds. These were discovered each year during the study period when the team collected the contents of the stomach.
It is also here that the DNA part comes into play, because it can be quite difficult to identify a bird when only half of it remains and it is covered. of shark bile.
Bird samples were sent to the Field Museum, where their DNA was sequenced and compared to a DNA database. The results were fascinating.
"None of them were gulls, pelicans, cormorants, or any type of marine bird," said marine ecologist Marcus Drymon of the United States. Mississippi State University. "They were all land birds."
Do not. A sailor. Bird.
Well, not identified, anyway. They only made conclusive positive identifications of 11 species of birds. There were eight singing bird passerines, two land birds near the passerines and a water bird (freshwater and non marine).
So how on earth did the sharks have these land birds? Well, an important clue was emerging when they ended up in the stomach of sharks.
Remember how the surveys were monthly? The researchers were able to define a peak season of birds for sharks, which coincided remarkably well with the time of year during which birds migrated near the place where sharks live.
All latecomers who fall into the water are easy choices.
"Tiger sharks recover singing birds that have difficulty flying over the ocean," Feldheim said. "During the migration, they are already exhausted, then they are tired or fall into the ocean during a storm.
At the same time, as seabirds already inhabit near ocean waters, they may be better able to fall overboard than a land bird, making them less easy to hunt.
This study is a sobering demonstration of the complex dynamics at play in the natural world and what we still do not know, not to mention that even changing small things could have repercussions that we can not even begin to envision. .
This could explain why so many shark populations, having swam in the ocean for hundreds of millions of years, are now dangerously threatened with extinction.
The search was published in Ecology.
[ad_2]
Source link